Method and apparatus for regulating the power supply voltage in motor vehicles

Abstract

For fuel economy, it is known that the engine of a motor vehicle may be turned off during vehicle operation while the electrical power for various appliances, such as the lighting circuit or the radio must be maintained. Upon restarting the engine, there may be a voltage drop in the vehicle supply circuit voltage with deteriorating effects in the lighting circuit and possibly failure of the radio. The disclosed circuit prevents such effects by limiting the rate of change of variations in vehicle supply circuit voltage as a function of connecting and disconnecting of a high-power component such as the starter.

We claim: 
     
       1. A method for controlling the vehicle circuit supply voltage in a motor vehicle having at least one high-power component and at least one low-power component in a low-power circuit and a main vehicle battery capable of being supplied by a generator comprising providing an auxiliary battery normally connected in parallel with the main vehicle battery and, when a high-power component is being supplied by the main vehicle battery, disconnecting the auxiliary battery from the main vehicle battery so that the voltage in the low-power circuit is drawn from the auxiliary battery to limit the rate of change of at least one of the vehicle current supply voltage and the voltage available in the low-power circuit. 
     
     
       2. A method according to claim 1 including connecting the main battery and the auxiliary battery in parallel to receive electrical energy from the generator when the engine is running and disconnecting the auxiliary battery when the engine is turned off so that the vehicle circuit is supplied by the main battery, and connecting the low-power circuit to the auxiliary battery and the high-power component to the main battery for starting the engine. 
     
     
       3. A method according to claim 1 including connecting the main battery and the auxiliary battery in parallel and supplying them with electrical energy from the generator when the engine is running and maintaining the main battery and the auxiliary battery connected in parallel after the engine has been turned off and disconnecting the auxiliary battery from the main battery and connecting it to supply the low-power circuit for starting the engine from the main battery. 
     
     
       4. A method according to claim 1 including connecting an auxiliary battery in series with the main battery when the high-power component is actuated so that the high-power component is supplied from the main battery and the low-power circuit is supplied by both batteries connected in series. 
     
     
       5. A method according to claim 1 including connecting an auxiliary battery of lower voltage than the main battery voltage in series with the main battery upon switching-off of the engine and/or starting of the engine and supplying the low-power circuit with voltage from both batteries connected in series. 
     
     
       6. A method according to claim 4 including maintaining the voltage supplied by the main battery and the auxiliary battery connected in series constant by a voltage regulator. 
     
     
       7. A method according to claim 4 including using the voltage in the main battery to define a reference voltage which follows the main battery voltage at a limited rate of change, and regulating the voltage of the series circuit according to the value of the reference voltage. 
     
     
       8. A method according to claim 1 including regulating the low-power circuit voltage to a selected value after the engine has been switched off. 
     
     
       9. A method according to claim 8 including using the voltage of the main battery to determine a reference voltage which follows the main battery voltage at a limited rate of change, and regulating the low-power circuit voltage according to the value of the reference voltage. 
     
     
       10. A method according to claim 8 including imposing a lower limit on the reference voltage. 
     
     
       11. A method according to claim 1 including limiting the rate of change of at least one of the low-power circuit voltage, the vehicle circuit voltage, and the reference voltage to 0.15 V/second. 
     
     
       12. Apparatus for controlling the vehicle current supply voltage in a motor vehicle containing an engine, a main battery, a generator, and at least one high-power component and a low-power circuit to supply voltage to at least one low-power component comprising control means for limiting the rate of change of voltage in the vehicle current supply circuit in response to operation of a high-power component, a low-power component, or the vehicle generator, the control means including an auxiliary voltage source arranged to be connectable in parallel with the main battery and switch means for connecting and disconnecting the auxiliary voltage source from the main battery. 
     
     
       13. Apparatus according to claim 12 including switch means for connecting the auxiliary voltage source to the low-power circuit when the high-power component is connected to the main battery. 
     
     
       14. Apparatus according to claim 12 wherein the auxiliary voltage source has a voltage rating which is about the same as the voltage rating of the main battery. 
     
     
       15. Apparatus according to claim 12 including an auxiliary voltage source arranged to be connectable in series with the main battery. 
     
     
       16. Apparatus according to claim 15 including switch means arranged to disconnect the auxiliary voltage source from the main battery when the engine is turned off. 
     
     
       17. Apparatus according to claim 15 including switch means for connecting the auxiliary voltage source in series with the main battery when the high-power component is connected to the main battery to increase the voltage available for the low-power circuit and voltage regulator means for controlling the output voltage of the voltage sources connected in series. 
     
     
       18. Apparatus according to claim 15 including voltage regulator means arranged to maintain the output voltage of the combined voltage sources constant. 
     
     
       19. Apparatus according to claim 15 wherein the auxiliary voltage source has a voltage rating between about half of the voltage rating of the main battery and the voltage rating of the main battery. 
     
     
       20. Apparatus according to claim 17 including regulating circuit means providing a reference voltage which is dependent upon the voltage of the main battery wherein the output voltage of the voltage regulator is capable of being adjusted to that reference voltage. 
     
     
       21. Apparatus according to claim 20 wherein the switch means is arranged to connect the auxiliary voltage source in series with the main battery when the engine is turned off. 
     
     
       22. Apparatus according to claim 12 including voltage stabilization circuit means capable of being connected in series with the main battery. 
     
     
       23. Apparatus according to claim 22 wherein the voltage stabilization circuit means includes regulating circuit means in which a reference voltage is produced which is dependent upon the voltage of the main battery and a voltage regulator with a DC--DC converter to provide a regulated voltage which is higher than the main battery voltage, and wherein the voltage at the output of the voltage regulator is capable of being adjusted to the reference voltage. 
     
     
       24. Apparatus according to claim 12 including means for turning off and starting the engine as a function of selected driving conditions.